The invention relates to a method for the production of three-dimensional attachments out of a flat strip by forming and fine blanking operations, especially attachments provided with formed parts inside such as projections and/or indentations and/or impressions and/or recesses and/or sinks and/or holes and/or pivots, especially for car seat components or the like, wherein the flat strip is fed into a tool, at least one plate with a substantially evenly curved outline is stamped out of the flat strip in the tool, the plate is processed into an attachment in multiple processing steps, at first by fine blanking, in a following second step the developed burrs are flattened and then, without finishing, the attachment is removed from the tool ready for mounting.
Furthermore, the invention relates to a tool for the production of three-dimensional attachments out of flat strips provided with formed parts inside, such as projections and/or indentations and/or impressions and/or recesses and/or sinks and/or holes and/or pivots, especially for car seat components or the like through combined forming and fine blanking processes with a tool for forming and fine blanking, a tool for flattening the burrs which developed at the inner and outer contours during fine blanking, and a transfer device for transporting the attachments between the tools.
Conventional seat adjustment components, for example fixed and swivelling hinge parts of hinge attachments, are produced by forming, fine blanking or stamping with the necessary high dimensional accuracy based upon final intended use. These hinge parts have inner or outer toothings for the transmission of rotational movements, which are formed in one piece together with the respective hinge part as projections (DE 32 44 399 C2, DE 28 34 492 C2, DE 32 27 222 C1).
EP 0 885 074 B1 discloses a method for the production of stampings, especially plates, in two operation steps. In a first operation step, the work part in a device is cut out of the starting material by fine blanking. After fine blanking, the work part is brought to the embossing stage by transfer tongs (accommodated in the device), wherein the embossing stage is also accommodated in the device. In a second operation step, the outer and inner contours of the work part are formed, so that the burrs developed at the work part during the first operation step are flattened to an extend that the work piece does not require further finishing.
Plates are disk shaped and have openings mostly in the form of slits, which are open towards the edge of the disk, or long holes (see DE 36 30 981 A1). Alternatively, they are closed disks having shafts projecting in an axial direction (DE 11 92 887). Plates without requirements with regard to tolerance do not make high demands on fine blanking processes and the portion of forming operations as drawing, bending, bending off, upsetting, cranking, surfacing, embossing, hobbing, making projections and indentations, extrusion or pressing pivots is not worth mentioning.
Regularly, attachments of car seat adjustments are provided with complex inner structures or contours such as projections, indentations, impressions, recesses, sinks, holes or pressed pivots, which place very high demands on forming and fine blanking processes with regard to the material, as well as to the design.
The limitations of fine blanking of portions with small corner radii in relation to the thickness of the sheet to be cut and to the quality of the material are sufficiently known. Based on experience, a fine blanking severity is defined which distinguishes the severity degrees S1 (easy), S2 (medium) and S3 (difficult) (see “Forming and fine blanking”, a handbook on cold pressing, material properties, component design, pages 154 to 165, Verlag Hallwag AG, 1997, Switzerland). Thus the severity degree is essentially defined by the cutting path geometry and the thickness of the metal sheet. For this, the cutting path geometry is divided into simple geometric basic areas such as corner radii, hole diameters, groove and fin widths. From the ratio between a geometric dimension and the thickness of the metal sheet results the severity degree of fine blanking, which grows with growing metal sheet thickness. This means that fine blanking of large-surface thin parts, as in the case of plates, is substantially easier than the fine blanking of small webs or rings in the case of large thickness of metal sheets. Also, obtuse-angled corners with big radii are to be cut better than sharp-cornered parts with small radii.
Due to the characteristic high portion of forming operations in connection with hinge attachments and their relatively large thickness, the state of the art according to EP 0 885 074 B1 is not transferable, because the necessary knowledge of the flow characteristics of the materials, the hardness and the stability of the extrusion ram under load, the coating, the lubricant and the design of the tool, is not available.
Furthermore, the state of the art according to EP 0 885 074 B1 has the disadvantage that the plates are only partially cut from the flat strip and thus in several points stay connected to the flat strip. Due to the different geometries in the flat strip eccentric loads occur, leading to a displacement of the strip, and thus to the impairment of the tolerances of the processed part, which is not acceptable for safety parts such as seat adjustment components. Furthermore, the disadvantage also exists in that due to the subsequent internal cut of the plate, still at some points connected to the flat strip, the circularity is heavily reduced, so that substantial deviations of tolerances may occur.
In view of this state of the art, it is a object of the invention to improve a method and a tool for producing attachments with complex geometry by combined fine blanking and forming operations in such a way that mountable and burr-free parts with very small tolerances, high accuracy and process safety can be provided at effective costs.